In the field of conventional writing instruments with a built-in replaceable ink cartridge, ink cartridges directly storing ink in a container having an open end and blocking the opening by a ball or a disk shaped plug are widely used. An ink-guidable tubular projection formed in a writing instrument body is engaged and connected to such cartridge from the front end opening, thereby press opening the plug. The ink in the container is thus introduced into the tubular projection to start ink supply to the pen point (for example, refer to Patent Documents 1 through 3).
Since a writing instrument of this type is capable of easily writing again, after ink in the ink cartridge is used up, by replacement with a new ink cartridge, it is widely spread in general from the perspective of high recycling and ink filling efficiencies of the writing instrument body.
However, when a used cartridge container is pulled out for ink cartridge replacement, the ink remained inside the container sometimes leaks to the outside depending on the speed of pulling out and the orientation of the container. In the structure of Patent Document 4, since the range of movement of a plug after the plug is opened is restricted, the above ink leakage does not easily occur relatively in comparison with other structures. In spite of that, the plug is freely movable in the plug opening state and thus makes contact with the container inner wall every time the plug moves to produce a noise. Further, when a strong impact such as falling occurs, the plug accelerated by the movement strongly collides with the connection portion and the container bottom wall, and thus deformation of the connection portion or lifting (shifting) or disengagement of the cartridge sometimes occurs, causing ink leakage.